The utilization of isogrid and/or orthogrid stiffening of advanced composite materials have been shown analytically and experimentally to exhibit some of the lowest weight designs for aircraft and spacecraft structures. Additionally, it has been found that isogrid and orthogrid stiffened composites exhibit excellent buckling performance. Currently, the manufacture of such known grid stiffened composite structures involves fabricating the skin plies and then building up the grid stiffening on the skin's inner mold line. However, the challenge and problem with this approach is that the grid is co-cured or bonded to the skin's inner mold line, which makes the grid susceptible to de-bonding from the skin as a result of impact damage to the skin's outer mold line. Thus, because of the poor damage tolerance characteristics of known grid stiffened composite structures, such grid stiffened composite structures are typically not capable for use on aircraft and spacecraft design despite the weight advantages.
Thus it can be seen that needs exist for improvements to grid stiffened composite materials that are low weight and exhibit high damage tolerance characteristics, such that the composite materials are capable of being used in aircraft and spacecraft designs. The composites and methods described herein address these needs.